Recommendations for emission testing and control of exhaust particles from a late technology mono-fuel CNG vehicle

Abstract

The current study characterizes sub-23nm volatile and non-volatile particle emissions from a late technology (Euro 6d-temp) port-fuel injection vehicle, operating with compressed natural gas (CNG) as the primary fuel and E10 gasoline, as a reserve fuel. In part of the testing, gasoline was replaced with alkylate fuel or was doped with an octane booster (MMT), to understand fuel impacts better. Alkylate use resulted to the lowest total particle number (TPN) emission levels, below that of the Euro 6 limit. Increased sensitivity to primary sampling temperature was observed for CNG due to the high H/C ratio that causes water condensation in the exhaust. A minimum sampling temperature of 70oC is recommended to avoid water particles in CNG operation. The study also assessed the potential of a particle filter (PF) in controlling total and solid CNG exhaust particles. Results indicate effective PF filtration of non-volatile and volatile particles, especially in the sub-23 nm size range. Gasoline and CNG tests with PF suggest TPN10 emissions in the order of 5 × 1011 p/km, below the Euro 6 and Euro 7 regulation limit. Adopting PF as part of the aftertreatment layout would be required for control of solid and total particle emissions from CNG vehicles.